Though it was originally marketed as the final episode of the first series, lack of new product as of 2018 has retroactively conferred a "series finale" status upon this episode.

It saw the revelation of the Department's creation and the true identity of its leader, Lomax. It also revealed that the recurring villain Thorne was working with the Korven. It featured the deaths of both characters.

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A strange phenomenon occurs in the space-time manipulator that heralds the Korven invasion. Thorne plots to help them and has as his back-up a secret weapon with K9's Regeneration unit augmenting it, making it indestructible. K9 faces his greatest foe yet. Gryffen and the youngsters face the unknown as the world itself seems doomed to destruction.

K9 watches as the STM activates, threatening to bring together a black hole and a white hole. As they come together, Starkey alerts Gryffen to the fact that it is happening again. Meanwhile, in the Department's base at the Millennium Dome, Thorne is excited. Gryffen tells Darius to tell June what's going on. Darius asks why it's dangerous to use his vid-com. Gryffen says they cannot risk the news being intercepted. Darius leaves as K9 advises they watch the STM; if the two objects align, it will mean catastrophe and the destruction of the planet. K9 says he has to go. Jorjie asks why his mission is more important than protecting the world. K9 assures them he should be back in twenty minutes; what he has to do is a matter of life and death. He must regain his regeneration unit.

K9 flies to the Millennium Dome and sees a non-functioning device similar to the STM. He is met by Thorne and his army of CCPCs. Thorne says he summoned K9. He wants him to do him a favour. The STM is a gateway and an invasion is about to occur. In Gryffen Manor, Starkey tries to contact K9 on vid-com, but there is no reply. The black and white holes are aligning. If they meet, the world will be destroyed.

Thorne tells K9 an invading army is massing on the other side of the galaxy. K9 asks if the Department has a plan to stop them. Thorne tells him that's where he comes in. He needs K9 to stabilise the gateway so they can launch a preemptive strike. K9 says that would require a temporal stabiliser and Gryffen has the only one on the planet locked away. Thorne informs K9 they have created a weapon, a supersoldier with the DNA of every species they've encountered: Jixen, Anubian, Meron, "you name it". K9 assumes it has been implanted with the regeneration unit. K9 asks for it back. Thorne says K9's small contribution will save the planet. K9 insists the weapon cannot work, but Thorne says it is working. The weapon has been in the room all along. K9 tells Thorne he has already detected him. Thorne introduces K9 to project: Trojan, who has decloaked.

At the mansion, Starkey tries to convince Gryffen to use the temporal stabiliser. When Jorjie says that they need K9, Gryffen is frustrated. Starkey says they can't wait. Gryffen warns it is too dangerous. K9's location was the Millennium Dome when communications ceased. Starkey and Jorjie go in search of K9 as Gryffen tells them to stay safe and that he is fond of them all.

At the dome, K9 confronts Trojan and demands his regeneration unit. At the Department Research Division, Darius finds June, who has been demoted to a constable after disobeying Lomax's orders. Starkey and Jorjie see all the CCPCs heading towards the dome. The deduce that something big is going on. Jorjie guesses K9 is involved. Inside the dome, K9 cannot move. Remote connection is in progress. He is wired to a cryo pod. Thorne says the reprogramming should be kicking in and K9 has taken to the connection very well. The remote connection is complete and space time portal generation commences.

At the mansion, Gryffen finds the portal is producing energy. Starkey and Jorjie follow the CCPCs to K9 inside the dome. Jorjie says K9 could be anywhere in the huge dome. Starkey wants to move on, but Jorjie reminds him of what Gryffen said about being fond. They start to kiss but are interrupted and chased away and pursued by CCPCs. K9 tells Thorne he fails to understand why opening a larger portal will prevent an invasion. He says it would allow an invasion instead. This means Thorne is working with the invaders. Thorne confirms this. K9 notes that the transferral system is too unstable. Thorne notes this is where Gryffen comes in.

At the mansion, Gryffen tries to contact everyone, but there is no reply. He refuses to let his planet be destroyed and takes the temporal stabiliser out of a safe. At the Research Division, June finds it hard to believe what Darius is saying. The Intelligence division would know about it. Their conversation is interrupted by two CCPCs saying that Department personnel no longer have any authority. June asks on whose orders. The CCPCs say it's classified; they are to subjugate all humans. June grabs a large gun, which she uses to destroy them. June and Darius peek out of her office and escape. The CCPCs are occupied restraining all other humans.

At the dome, Starkey and Jorjie find K9 with Thorne waiting for them with the decloaking Trojan. K9 apologises to Starkey. Starkey asks Thorne what he has done to him. Thorne tells him he's been put to good use and that they're about to receive company; if Gryffen doesn't use the stabiliser, the entire planet will disappear in thirty seconds. Gryffen uses the temporal stabiliser and gets a nasty surprise when the STM fluctuates. K9 announces maximum danger as the invaders arrive. They are the Korven. The vanguard of four arrive, claiming the planet in the name of the supreme leader of the pan-dimensional army, Lomax. Thorne informs Lomax the prototype for the supersoldier is ready. Jorjie asks Thorne how he could betray his planet. Thorne says he isn't strictly from this planet. He explains that the Korven implanted MeronDNA in him. Lomax says the Korven were the Meron's allies in the war against the Jixen, just as Jixey told Starkey. He says they needed an ally on Earth to prepare the way for them. Starkey says it must have taken a lot of convincing. Thorne tells him he's always made it a policy to be on the winning side and the Korven are the winning side.

At the mansion, Gryffen wonders what he has done, then asks what he's going to do now. As June and Darius run, June starts to the mansion, thinking Jorjie is there. Gryffen records a message against his failure, saying his friends are in danger and he can't reach them. He says he believes he is their only hope of survival and "that of the entire human race: me, an agoraphobic, reclusive shut-in." He says this video means that he didn't just sit in the house as he has for so long. "Alistair Gryffen finally stood up and did something." He leaves his house with determination.

Back at the Dome, Lomax decides K9 is not fit for battle. Starkey says he could be free from the pod. Thorne tells him K9 wouldn't hurt a human. He says the Korven couldn't reprogram him to eliminate Jixen and Gryffen. Starkey asks why they'd want to kill Gryffen. Lomax explains that he is the only one that could prevent the invasion; he knows the code to terminate the portal permanently, but it's a voice activated code. He'd have to be here to say it in person and that would never happen... just as Gryffen races into the dome. Lomax announces the army's arrival is imminent and orders his guards to prepare. Jorjie and Starkey go to K9. Starkey asks him if he can terminate the program. K9 tells him that the Korven override program is too strong. He says the only possibility is to get a message to Gryffen to use the portal termination code. All communications are down, but K9 is connected to the STM.

Starkey tries to contact Gryffen, but he isn't in the mansion. Darius and June arrive in the mansion and hear Starkey transmitting. Thorne says even if he got through, Gryffen would never terminate the STM; without it he'd never see his family. Gryffen reveals himself above the stairs and Thorne taunts him about his family and asks him what their names were. Gryffen says their names and follows the names with says the Greek letters, "Omega, Sigma, Theta, Ohm". Thorne asks if they were pets. Gryffen says that's the voice-activated termination code. The portal activates in the mansion. Darius pulls June back as K9's remote link is severed. Gryffen tells Starkey and Jorjie to get down. Lomax and the Korven are sucked into the portal and destroyed as it explodes.

Thorne warns Gryffen he's meddled for the last time and tells Trojan to kill them all. K9's visual sensors are offline, so he switches to olfactory sensors and fires at Trojan. Thorne orders Trojan to finish K9. K9's power levels are too low for his laser to work. He lets out a wail. Thorne is amused that K9 is crying but he isn't crying, he's shrieking the Jixen battle shriek. Gryffen and Starkey say he's calling the Jixen to do battle against the Meron. Trojan becomes a creature at war with itself as its Jixen and Meron DNA fight each other. Starkey and Jorjie tend to K9 when he doesn't reply. Thorne tells them to not think they've seen the last of him before Trojan collapses on him. Gryffen averts his eyes as Thorne is crushed to death.

Back at the mansion, June and Darius regain consciousness. Darius helps her up. June thanks Darius for saving her life. Darius insists it's just what he does but June says there is something more to him than that. If the Department survives, she can use someone like him. Jorjie arrives and June is grateful she is alright. The team stand in the STM room, looking on at K9. Gryffen tells them there's nothing he can do. K9 has exhausted his core energy. Starkey compares it to when he first came here. Gryffen notes the difference is he doesn't have his regeneration unit. Darius insists he can self-repair and has done it before, but Gryffen tells him not this time. Gryffen and June leave the kids in peace with K9. Darius tells K9 that he's the coolest thing that has ever happened to him. Jorjie kneels down to K9 and tells him about all those times she tried to teach him to have fun and how she's had a lot of fun since she met him.

A "friskier" K9

Finally, Starkey goes to him and tells him that he's right. He's not a dog. He's Starkey's best friend. He used to think he was brave but K9 made him fearless. Starkey pulls K9's head up and tells him he's going to miss him. K9 remembers Starkey's first words to him and utters his final words, "Yes, young master". Starkey takes off his coat and puts it over K9. As he stands, he finds the regeneration unit materialising in his hand, then disappearing. After a short look for it, they notice a flicker of movement in K9. Starkey calls for K9, who pops out of the coat and affirms, wearing his original dog collar. Gryffen and June walk in, overjoyed with the kids. K9 explains his regeneration unit has homed to him due to its programming. He tells them he feels frisky and flies up as the team watch him, delighted. Starkey asks him if he's back in business. K9 cheerfully replies, "Affirmative".